1. Field of the Invention
The invention relates to a single chip embedded microcontroller (smart card integrated circuit) using FLASH array technology to create multiple non-volatile erasable PROMS which share a single high voltage generator. More particularly, the FLASH array technology allows an EEPROM and OTPROM to have similar erase and write voltages and therefore to share the high voltage generator.
2. Description of the Related Art
Smartcard devices are single chip systems that are self contained and need only an energy supply and a serial interface to function. The supply is either obtained by contacts from the reader, or by an electromagnetic field. In both cases the voltage that the device uses is low, for example 3v. or 5v., to minimize the power consumed. However, non-volatile memory technologies on the smart card require voltages 2 to 3 times that of the other circuit elements. This has to be supplied to allow the erasing and writing of these non-volatile memories. The specification for ISO compatible contacting devices does specify a pin to supply the voltage for the non-volatile memory, but this is no longer used on the grounds of security. Smart card devices have on board voltage converter circuitry, to produce the high voltage required by the non-volatile memory. These are large and electrically noisy and add to the cost of the device. If both non-volatile EEPROM (electrically erasable programmable read only memory) and OTPROM (one time programmable read only memory) memories are used on the smart card then multiple voltage supplies and decode logic are needed to support the memories. The reason is that different technologies may be used to create the EEPROM and OTPROM arrays and hence different erase and write voltages are needed.
It would be desirable to have a smart card with multiple non-volatile erasable PROM arrays that operate independently and still share one high voltage power supply to provide the high voltage required for erasing and writing.